Machine for piercing a taphole for a shaft furnace

ABSTRACT

A machine is provided for piercing a taphole for a shaft furnace for applying the piercing rod method. The machine comprises a mounting (20), a drive means (42, 44), a clamp (34) for coupling the drive means to the rod (26) during its extraction. It is characterised by a push-member (34) transmitting the said thrust force to the rear end of the rod (26) during the insertion of the rod (26) into the taphole clay and by intermediate guides (55i) surrounding the rod (26) at several places during the insertion of the rod (26) into the taphole clay. The said guides (55i) being successively placed in a position in which they do not hinder the advance of the said push-member (34, 78) on the mounting (20).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a machine for piercing a taphole for ashaft furnace, designed for the implementation of the method called"lost rod method" in which, after having blocked the taphole with ataphole clay, a metal rod is driven into this clay, before it has fullyhardened, and it is extracted, at the desired time, with a view toopening the taphole. The said machine comprises a mounting forsupporting the rod during the said method, a drive means mounted on themounting so as to develop a traction force or thrust force respectivelyparallel to the mounting, a coupling member for coupling the said drivemeans to the rod so as to transmit the said traction force to it duringits extraction.

Prior Art

The machines used until now for the implementation of this lost rodmethod are, in principle, conventional drilling apparatuses, that is tosay drilling apparatuses designed for working with a drill bit, whichhave however undergone appropriate adaptations and modifications for theimplementation of the method.

The working member of these machines, which normally serves to drive acutting drill bit rotationally, must include a coupling clamp for therod and, especially, a powerful bidirectional pneumatic hammer fordelivering the energy necessary for the insertion and extraction of thepiercing rod according to the said "lost rod method".

From the document FR-A-2,520,857, a clamp is known which is designed tobe mounted on the bidirectional hammer drilling apparatus of aconventional taphole piercing machine. For the operation of extracting apiercing rod embedded in the taphole clay, the normal coupling of thedrilling apparatus, serving to communicate a rotational movement to adrill bit, is exchanged with this clamp. The latter then makes itpossible to couple the drilling apparatus to the rear end of thepiercing rod and to withdraw it by actuating a powerful hammer integralwith the drilling apparatus.

In most cases, these piercing machines also preserve the possibility ofbeing able to use the drilling apparatus with a conventional drill bit,either for reforming or moving the taphole, or for drilling the holeconventionally when the lost rod method cannot be used for one reason oranother. However, in order to drill the taphole with a conventionaldrill bit, it is necessarily required to exchange the clamp with thenormal coupling of the drilling apparatus, since the jaws of the clampare not suitable for transmitting a rotational movement to a drill bit.

It will be noted that a powerful hammer, as is used on these machines,is not without disadvantages. Firstly, it exerts considerable stressesand vibrations on the equipment particularly on the rod-coupling clamp,which is, as a result, subjected to rapid wear. It is also extremelynoisy, and often does not conform to the ever-stricter standards aimingto reduce the noise level in an industrial environment.

The disadvantages of the hammer could consequently make it desirable toeliminate the percussion during the insertion and extraction of the rod.

From the document EP-A-0,379,018, a piercing machine is known for theimplementation of the "lost rod method" which does not use a hammer forthe extraction of the rod for piercing the hardened taphole clay. Forthis purpose, the machine proposed uses a clamp which can move towardsthe front of the mounting by means of a powerful hydraulic jack whosestroke is, for size-requirement reasons, substantially smaller than thelength of the piercing rod to be extracted. This jack causes the clampto perform several strokes in the vicinity of the front end of themounting in order to extract the rod by its complete length from thetaphole. It follows that the extracted piercing rod--which is hot,deformed and clogged-up--must pass entirely through this extractionclamp. In addition, the extraction clamp is exposed to the projectedsplashes from the taphole as soon as it is opened. The documentEP-A0,379,018 contains no indication how it would be possible to insert,without a hammer, the piercing rod into the taphole clay injectedbeforehand into the taphole.

The document EP-A-0,379,018 consequently provides only one imperfectsolution for the extraction, without a hammer, of the piercing rod andno solution at all for the insertion of the piercing rod, without ahammer, into the taphole clay.

SUMMARY OF THE INVENTION

The aim of the present invention is to provide a machine for piercing ataphole for a shaft furnace, which is designed for an implementation ofthe "lost rod method", and which makes it possible to dispense with apowerful bidirectional hammer, both for the extraction of the piercingrod from the taphole clay and for its insertion into the taphole clay.

According to the present invention, this objective is achieved by amachine for piercing a taphole for a shaft furnace, comprising

a mounting for supporting either a piercing rod or a drill bit, the saidmounting comprising a front end which may be arranged facing the tapholeand a rear end axially opposite the front end,

a drilling apparatus with a coupling which is designed to receive androtationally drive the drill bit, the said drilling apparatus beingmounted so as to slide on the mounting,

a drive means mounted on the mounting so as to develop a traction forceor thrust force respectively, parallel to the mounting,

a clamp mounted on the mounting between the front end of the latter andthe drilling apparatus and connected to the drive means, the said clampcomprising a body which is traversed axially by a channel which has adiameter slightly greater than the rod and the drill bit, movable jawswhich are arranged around the channel and which are designed so as to beable to grip the rear end of the rod engaged in the channel in order totransmit to it a large traction force when the clamp is moved in thedirection of the rear end of the mounting,

characterized

in that the clamp can be moved by the said drive means along themounting over a length which corresponds approximately to the length ofthe rod,

in that a key can be engaged in a housing in the body of the clamp so asto block the channel axially and to be able to transmit, to the rear endof the rod engaged in the channel, an axial thrust force when the clampis moved in the direction of the front end of the mounting,

in that the said key, when it is withdrawn from its housing, frees thechannel in the clamp so as to be able to pass through this channel withthe drill bit and to couple the latter to the coupling of the drillingapparatus located between the clamp and the rear end of the mounting,

in that intermediate guides are mounted on the mounting between thefront end of the latter and the clamp, the said guides having, on themounting, operating positions in which they surround the rod at severalaxially spaced-apart places during its insertion into the tapholeblocked beforehand with the taphole clay, and parked positions in whichthey do not hinder the advance of the said clamp towards the front endof the mounting, and

in that these intermediate guides are capable of moving, as the clampadvances towards the front end of the mounting, from the said operatingpositions into the said parked positions.

According to a main characteristic of the present invention, the metalrod is guided, during the insertion operation, by intermediate guidesmounted on the mounting and surrounding the rod at several places. Theseintermediate supports prevent the rod from starting to buckle when aconsiderable axial thrust is applied, by the sliding clamp, providedwith its key and driven by a powerful drive means, at one end of the rodin order to drive its opposite end into the taphole clay with which thetaphole has been blocked beforehand.

It will be noted that intermediate supports on the mounting of apiercing machine are already known for other reasons.

The document GB-A-2,095,381 discloses a piercing machine provided withan intermediate support between a percussion drilling apparatus and thefront bearing surface of the piercing machine. The purpose of thisintermediate bearing surface is to avoid a cantilevered support of apiercing rod or of a drill bit in the coupling of the processiondrilling apparatus. Such a cantilevered support could possibly arise ifthe front end of the piercing rod or of the drill bit were consumed inthe taphole. It will also be noted that the above-mentioned documentexplicitly recommends the insertion of the piercing rod into theblocking clay by means of a hammer integral with the drilling apparatus.

The document US-A-5,069,430 relates to a machine for piercing a tapholefor a shaft furnace, which is equipped exclusively for drilling thetaphole by means of a rotary drilling apparatus driving a drill bit witha cutting head. More specifically, it is proposed to work with a drillbit comprising several rod segments coupled to each other. In order toprevent these coupled segments from sagging, when the drill bit issupported on the mounting of the machine, it is proposed to support thedrill bit, between the front bearing surface and the drilling apparatus,by a movable support attached to an endless chain. Too great a sag ofthe drill bit supported on the mounting would, in effect, make the drillbit deviate from its ideal drilling path.

It is important here to note that the drilling of the taphole does notat all give rise to the same problems as the method of opening thetaphole by means of a piercing rod embedded in the taphole clay. Thereason for this is that the axial forces which the drilling apparatusmust transmit to the drill bit are completely negligible in comparisonwith the forces to be transmitted to the piercing rod in order to insertthe latter into the taphole clay, respectively compared to the tractionforces to be transmitted to the rod in order to extract the latter fromthe hardened taphole clay. The document US-A-5,069,430 could thereforeprovide no contribution to solving the problem which is the basis of thepresent invention.

The main advantage of the present machine is to be able to insert therod in one stroke into the taphole clay without having to use a noisyhammer subjecting the equipment and the machine to considerablevibration stresses.

Another advantage of the present invention resides in the fact of beingable to extract the piercing rod from the taphole clay by coupling theclamp to the rear end of the rod and by subsequently withdrawing theclamp towards the rear end of the mounting.

An additional advantage of the machine according to the invention isthat it is not necessary to dismantle the clamp, serving for theapplication of the said "lost rod method", when it is desired to drillthe taphole by means of a conventional drill bit.

When, during the insertion of the piercing rod into the taphole clay,the clamp advances towards the front of the mounting as the rod isprogressively driven into the taphole clay, the said circumferentialguides must be removed one after the other, since they would hinder theadvance of the clamp on the said mounting.

This may be done manually for example, by each time stopping themovement of the clamp just before it reaches the guide which it riskshitting, by dismantling this guide, and by continuing the insertionmovement of the rod up to the following guide.

The present invention, however, also provides preferred solutionsenabling the said guides to be put automatically, that is to say withoutstopping the insertion movement and without any intervention by themachine operator, into a position which does not hinder the clamp as itadvances towards the front of the mounting.

In a preferred embodiment, the said guides can for this purpose slide onthe mounting. It will then be possible to provide them with a specificdriving system for driving them towards a parked position, at the frontof the mounting, as they progressively risk hindering the advance of theclamp. However, they could also be advantageously driven or pushed, bythe means for driving the clamp or by the clamp itself into a parkedposition at the front of the mounting as the clamp advances.

It will be appreciated that the present invention also providespreferred solutions for automatically rearranging the said guidessliding on the mounting in their initial operative position, that is tosay that which corresponds to the start of the rod insertion operation.

In an alternative embodiment, the said guides each consist of two halvessurrounding the rod circumferentially, when they are assembled, over acertain length. When the clamp risks hitting such a guide, the twohalves are moved apart laterally by appropriate means, thus freeing thepath of the clamp. These guides have the advantage that they do notrequire, in principle, any parked position at the front of the mounting.

The driving means adopted for the clamp preferably comprises one or moreendless chains mounted on the mounting and driven by at least onepowerful motor, whose direction of rotation may be reversed so as toensure both the rod insertion operation and the rod extractionoperation. It is however also conceivable to produce these driving meanswith hydraulic jacks or a screw and nut system, or a combination ofseveral of these systems.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages and characteristics will emerge from the detaileddescription of an advantageous embodiment, described below, by way ofexample, with reference to the attached drawings in which:

FIG. 1 shows the longitudinal section of a first embodiment of theproposed machine, at the start of the operation of inserting a rod intothe taphole clay;

FIG. 1a shows a plan view of the machine according to FIG. 1;

FIG. 2 shows a longitudinal section of the machine according to FIG. 1,after the rod insertion operation is finished;

FIG. 3 shows an elevation of a variant of the proposed machine, at thestart of the operation of inserting a rod into the taphole clay;

FIG. 4 shows a preferred embodiment of an intermediate guide;

FIGS. 5 and 5a show partial sections across a preferred embodiment of aclamp during the rod insertion operation, the sectional planes of the 2figures being at 90° to each other.

FIGS. 6 and 6a show sections identical to the FIGS. 5 and 5a, during adrilling operation with a conventional drill bit.

All the Figures comprise the same reference numbers for designating thesame components.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

For the description of the construction of the machine, FIGS. 1 and 1aare referred to. The framework of the piercing machine consists of amounting 20. This mounting is, for example, supported in a conventionaland known manner at the end of a supporting arm (not shown). Thissupporting arm may pivot about a bracket in order to move the piercingmachine between a parked position and an operative position and viceversa.

The mounting 20 may for example be formed by two parallel beams 20a, 20bjoined together. On FIG. 1, only the beam 20a can be seen, the beam 20bhaving been left out in order to show more details. The two beams 20aand 20b comprise, on their inner face, two rails 22 and 24 arrangedface-to-face. Only the rail 22 is shown in FIG. 1.

Reference 26 designates a piercing rod, still called "lost rod", used inthe said lost rod method described in the preamble.

At the front of the machine there can be seen a support 28 which ispreferably a screen-support of the type provided by the European PatentApplication EP 0,064,644. This support comprises two flaps mounted atthe front of the mounting 20, that is to say opposite the taphole whenthe machine is in the operative position. These flaps can pivot betweenan open position facilitating the engagement and the grasping of the rod26 with a view to extracting the latter and a closed position in whichthey define an opening for supporting the rod 26. The two flaps thusconstitute a support and at the same time form a shield providingprotection against the splashes originating from the jet coming out ofthe taphole when the latter is opened.

At least one endless chain 44 is mounted parallel to the rails 22 and24, between the two beams 20a and 20b. This chain 44 is tensionedbetween a driven toothed wheel 45 mounted at the front of the mounting20 and a driving toothed wheel 46 mounted at the rear of the mounting20. The driving wheel 46 is driven by at least one motor 42, fixed ontothe mounting 20.

This is preferably a hydraulic motor whose direction of rotation can bereversed by an adapted control system.

Reference 34 designates a clamp intended for the insertion andextraction of the rod 26. This is preferably the clamp described below.The clamp 34 is supported by a carriage 36 sliding freely along themounting 20, for example by means of runners 37 guided in the rails 22and 24 which are mounted on the two beams 20a and 20b of the mounting20. The carriage 36 is fixed to the endless chain 44 and can be drivenby the latter between a stop-piece 50 mounted at the front of themounting 20 and a stop-piece 51 mounted at the rear of the mounting 20and vice versa. The travel between the two stop-pieces 50 and 51 isapproximately equal to the length of the rod.

It can be seen in FIG. 1 that the carriage 36 can also support a workingmember 32. This working member which is provided with a coupling 30 fora conventional drill bit usually comprises a rotary percussion drillingapparatus. Its presence is justified in order to be able to drill ataphole, if need be, with the conventional drill bit. It should,however, be emphasized that the working member 32 is not used in thelost rod method and that it could be removed if the conventionaldrilling of the taphole is never used, or if this drilling can becarried out in another manner. Of course, the working member 32 couldalso be provided with its own carriage and its own driving means.

Other characteristics of the machine according to the present inventionwill now be described and its operation for inserting the rod 26 intothe taphole and for extracting it therefrom will be studied at the sametime.

The rod 26 is preferably loaded into the machine when the latter is inthe parked position and when the clamp 34 occupies a position at therear of the mounting (cf. FIG. 1).

The loading is performed by passing the rod 26 into the clamp 34 and byinserting it into several intermediate guides (55₁, 55₂, 55₃), which areplaced at several places which are spaced almost equidistantly on themounting 20.

The purpose of these guides (55i) is to prevent the rod 26 from bucklingwhen the clamp 34 applies an axial thrust on it during the insertionoperation.

It should be noted that the number of intermediate guides as well astheir spacings will be determined as a function of the characteristicsof the rod (diameter, length, material, etc) and of the force necessaryfor inserting the rod 26 into the taphole clay. This force isessentially determined by the characteristics of the taphole clay and,inter alia, by its hardening rate.

In order to be effective, each guide (55i) must surround the rod 26 insuch a way as to prevent the latter from escaping laterally when it issubjected to an axial thrust at its opposite end to the taphole. Inaddition, the distance between two successive guides must not be toolong, else there is a risk of the rod 26 buckling between two guides(55i), which could ultimately result in the rod being completely jammedbetween these two guides.

In order to be able to apply the present method during the insertion ofa rod, it is necessary successively to remove the said intermediateguides (55₁, 55₂, 55₃) from the path of the clamp 34 as it advancestowards the front of the mounting 20. This is not a problem per se forthe success of the present method, since the more the clamp 34 advances,the more the length of the rod decreases and fewer intermediate guidesare required. It would, however, be tiresome to stop the advance of theclamp 34 each time in front of a guide in order to dismantle the lattermanually. The present invention thus presents solutions forautomatically removing these intermediate guides when the clamp 34advances towards the front of the mounting 20 in order to drive theguided rod, by means of an axial thrust on its free end, into thetaphole clay.

In a first solution, it is proposed to use guides arranged in a slidingmanner on the mounting 20. These guides (55₁, 55₂, 55₃) will then bepushed by the clamp 34 or the carriage 36 towards the front of themounting 20 as the rod 26 is progressively inserted, that is to say asthe clamp 34 advances.

That is to say that the carriage 36 first encounters the guide 55₃ onits path, it bears on the latter and pushes it in front of itself. Aftera certain distance, the guide 55₃ bears on the guide 55₂ and thecarriage now pushes the two guides 55₃ and 55₂ in front of itself. FIG.2 shows the end of the insertion operation. The carriage 26 is stoppedagainst the stop-piece 50 and the three intermediate guides 55₁, 55₂,55₃ are located, one against the other, in a parked position in front ofthe carriage 36.

FIG. 3 shows a preferred embodiment of a sliding guide. It comprises ahook 56 which is, for example, engaged with grooves in its foot 57between the lower flanges of the beams 20a and 20b forming the mounting.It is to be noted that the mounting of the hook must allow the latter toslide on the mounting 20, while preventing the hook from twisting whenit is subjected to out-of-line forces.

In order to be able to house the rod 26 easily in the hook 56, thelatter comprises a lateral notch defined by two horizontal edges whichare spaced apart by a distance which is slightly greater than thediameter of the rod 26. Before starting the operation of inserting therod 26 into the taphole clay, this lateral notch is closed by means of acomponent 58 which is perpendicular to the two horizontal edges, so asto surround the rod 26 closely and prevent the latter from escapinglaterally out of the hook 56. The component 58 may be articulated ontothe hook 56 and may be advantageously provided with a handle 59 easilyso as to be able to open and close the said lateral notch manually. Itwould however also be possible to fully automate this opening andclosing of the said notch.

In a variant of the embodiment of the said guide, the latter consist oftwo symmetrical halves which may be moved laterally away from the rods26 during the approach of the clamp 34. This variant is strictlyequivalent, with regard to operation, to the sliding guide variantdescribed above; it will therefore not be described in detail below.

It will be appreciated that the present invention also provides apreferred embodiment which enables the guides (55i) to be brought fromtheir parked position at the front of the mounting, which they occupy atthe end of the operation of inserting the rod into the taphole clay, totheir operative position which they must occupy at the start of the saidinsertion operation.

FIG. 1 shows for this purpose fingers 53₁, 53₂, 53₃ which are spacedequidistantly and are firmly attached to the chain 44. These fingersbear on the sliding guides 55₁, 55₂, 55₃ when the chain 44 is put intoreverse, that is to say when the carriage 34 is brought from the frontof the mounting towards the rear of the mounting. This device thereforeenables the sliding guides 55₁, 55₂, 55₃ to be rearranged automaticallyat the end of the rod insertion operation, by a simple withdrawal of thecarriage 36. A similar effect may furthermore be obtained by joining thesliding guides 55₁, 55₂, 55₃ together and to the carriage 36 by means ofrods 54₁, 54₂, 54₃, guided in eyelets 60, 60' which are firmly attachedto the hooks 56 (cf. FIGS. 3 and 4). These rods could of course bereplaced by chains or telescopic rods.

The clamp 34 which is preferably used on a machine according to thepresent invention is shown in FIGS. 5, 5a, 6 and 6a.

This clamp 34 comprises a clamp body 75 which is traversed axially by abore or channel 74 having a diameter which is slightly greater than therod 26. It can be seen that this is a unidirectional clamp designed forextracting the rod 26, that is to say that it comprises 2 jaws 70, 72arranged symmetrically around the actual channel 74 and capable ofmoving obliquely towards the axis of this channel 74 in the direction ofthe front of the mounting. The result of this is that under the effectof traction towards the rear of the mounting, allowing the rodextraction operation, the jaws 70, 72 automatically clamp onto the endof the rod 26 placed in the channel 74 and thus provide a perfectcoupling of the clamp 34 with the rod 26. This is however not the caseduring the insertion of the rod.

By virtue of a clever system provided by the present invention, thisunidirectional clamp may however also be used with the present machinefor inserting the rod 26 into the taphole clay. For this purpose, thepresent invention proposes to install a mechanical stop in the channel74, behind the jaws 70, in order to provide a bearing point for the rod26 during the said insertion operation.

It is more precisely proposed to produce this mechanical stop in thechannel 74 in such a way that it is easily removable. It is thuspossible to pass through the said clamp 34 with a conventional drill bit27, when it is necessary to drill with the working member 32 placedbehind the clamp 34, as shown in FIGS. 6 and 6a.

FIGS. 6 and 6a show that this movable mechanical stop is produced byinserting a key 78 into a slot 76 which passes perpendicularly throughthe channel 74. This key 78, whose height is slightly greater than thediameter of the rod 26, is secured at 80 so as to prevent anyinadvertent displacement. It is, however, also conceivable to producethis mechanical stop by means of a key 78 actuated, for example, by apneumatic circuit, which would avoid the need for any human interventionon the clamp itself in order to close or open the said channel 74.

FIGS. 6 and 6a show that for a drilling operation, the said key 78 isremoved. The drill bit 27 may thus pass through the clamp 34 so as to beinserted into the coupling 30 of the working member 32, where it islocked by an anti-rotation stop 80.

Returning to the method of the lost rod, and more precisely to theoperation of inserting the rod 26 into the semi-hardened taphole clay,it is noted that when the rod 26 is passed into the clamp 34 in whichthe key 78 is in position, and when all the intermediate guides areproperly arranged and closed, the motor 42 may be actuated in order toadvance the clamp 34 and thus push the rods 26 into the taphole clay. Inview of the fact that the rod 26 is surrounded at several places by theguides 55₁, 55₂, 55₃, it is not likely to buckle, even though it issubjected to a considerable axial thrust force. As the carriage 36advances, the rod 26 is driven into the taphole clay, and theintermediate guides 55i which hinder this advance are either pushedforwards, as described above, or moved apart laterally.

For the operation of extracting the rod 26, the free end of the latteris passed through the clamp 34 which is at rest against the stop-piece50. The clamp 34 is closed by actuating the jaws 70 and 72 which gripthe said end of the rod. The motor 42 is then actuated in order to pullthe carriage 36 towards the stop-piece 51. There is, of course, no needfor intermediate guides 55₁, 55₂, 55₃, since the rod is not subjected toa compression but to a traction. These guides are used only asintermediate supports for the rod as the latter is progressively pulledout of the taphole. It is also important to note that during the lastphase of extraction, the screen-support 28 is preferably closed so as toprotect the front of the mounting from splashes.

The present invention provides a machine which enables a piercing rod tobe inserted into the taphole clay without using a hammer, by exerting asimple powerful axial thrust on the end of this rod, which was judged tobe inconceivable until now. In addition, this machine is distinguishedby a simple and robust design, and it will be further appreciated thatit provides a better protection of the environment with an almost silentoperation.

We claim:
 1. Machine for piercing a taphole for a shaft furnace,comprising:a mounting for supporting either a piercing rod or a drillbit, the said mounting comprising a front end which may be arrangedfacing the taphole and a rear end axially opposite the front end, adrilling apparatus with a coupling which is designed the receive androtationally drive the drill bit, the said drilling apparatus beingmounted so as to slide on the mounting, a driver mounted on the mountingso as to develop a traction force or thrust force respectively, parallelto the mounting, a clamp mounted on the mounting between the front endof the latter and the drilling apparatus and connected to the driver,the said clamp comprising a body which is traversed axially by a channelwhich has a diameter slightly greater than the rod and the drill bit,and movable jaws which are arranged around the channel so as to be ableto grip the rear end of the rod engaged in the channel in order totransmit to it a large traction force when the clamp is moved in thedirection of the rear end of the mounting, wherein the clamp can bemoved by the said driver along the mounting over a length whichcorresponds approximately to the length of the rod, and wherein a keycan be engaged in a housing in the body of the clamp so as to block thechannel axially and to be able to transmit, to the rear end of the rodengaged in the channel, an axial thrust force when the clamp is moved inthe direction of the front end of the mounting, and wherein the saidkey, when it is withdrawn from its housing, frees the channel in theclamp so as to be able to pass through this channel with the drill bitand to couple the latter to the coupling of the drilling apparatuslocated between the clamp and the rear end of the mounting, and whereinintermediate guides are mounted on the mount between the front end ofthe latter and the clamp, the said guides having, on the mounting,operating positions in which they surround the rod at several axiallyspaced-apart places during its insertion into the taphole blockedbeforehand with the taphole clay, and parked positions in which they donot hinder the advance of the said clamp towards the front end of themounting, and wherein these intermediate guides are capable of moving,as the clamp advances towards the front end of the mounting, from thesaid operating positions into the said parked positions.
 2. Machineaccording to claim 1, wherein the said guides can slide on the mounting.3. Machine according to claim 2, wherein the said intermediate guidesare mounted on the mounting so as to be pushed by the said clamp fromtheir initial operating position to a parked position at the front ofthe mounting, as the said clamp advances towards the front of themounting.
 4. Machine according to claim 3, wherein each intermediateguide can be driven by the said driver from the parked position at thefront of the mounting to its initial operating position, as the saidclamp retreats from the front towards the rear of the mounting. 5.Machine according to any one of claim 1, wherein the said intermediateguides consist of hooks, sliding on the mounting and provided with alateral notch enabling the rod to be housed therein, and wherein thesaid lateral notch is provided with a component enabling it to be closedlaterally after the rod has been housed therein.
 6. Machine according toclaim 1, wherein the said driver mounted on the mounting comprises atleast one endless chain installed on the mounting and at least one drivemotor whose direction of rotation may be reversed.
 7. Machine accordingto claim 6, wherein the motor is a hydraulic motor.
 8. Machine accordingto claim 1, wherein the clamp and the drilling apparatus are supportedby a common carriage which can slide in rails of the mounting,andwherein this carriage is connected to the said driver.
 9. A machinefor piercing a taphole for a shaft furnace, comprising:a mountingadapted to support one of a piercing rod and a drill bit at selectedtimes, said mounting including a front end and a rear end, said frontend being arranged facing the taphole and the rear end being axiallyopposite the front end; a drilling apparatus slidably engaged on saidmounting and adapted to rotationally drive a drill bit when a drill bitis utilized; a clamp moveably mounted on said mounting between saiddrilling apparatus and the front end of the mounting, said clampcomprising a body, having an axial channel, said channel having adiameter slightly larger than the drill bit or piercing rod extendingwithin said channel, said channel further including a pair of moveablymounted jaws, capable of gripping a rear end of a rod introduced in saidchannel, so that said rod can be withdrawn from the taphole when theclamp is supplied with a motive force towards the rear end of themounting, said clamp further including a housing; a key associated withsaid housing, said key being engageable in said housing to block saidchannel, so as to enable a motive three towards said front end of saidmounting supplied to said clamp to be effectively transmitted to the rodto urge the same into the taphole, said key further being disengageablefrom said housing to allow the through-passage of the drill bit, so thatsaid drill bit may interconnect with said drilling apparatus, and adriver operatively connected to said clamp so as to supply said motiveforce towards the rear end of the mount, respectively said motive forcetowards the front end of the mount.